Swellable polymer with cationic sites

ABSTRACT

The invention is directed to long lasting crosslinked water-soluble swellable polymers, methods for making same, and their uses. More particularly, the invention relates to a composition comprising expandable polymeric particles having cationic sites as well as labile crosslinkers and stable crosslinkers, said particle mixed with a fluid. A particularly important use is as an injection fluid in petroleum production, where the expandable polymeric particles are injected into a target zones in the reservoirs and when the heat and/or a suitable pH in the reservoir cause degradation of the labile crosslinker and when the particle expands, the cationic sites in the polymer adsorb to negative sites of the rock in the formation, thus diverting water to lower permeability regions and improving oil recovery. However, many other uses are possible.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Divisional Application of U.S. application Ser.No. 12/815,314, filed Jun. 14, 2010, which claims priority to U.S.Provisional Application No. 61/186,957, filed Jun. 15, 2009. Bothapplications are incorporated herein by reference in its entirety.

FEDERALLY SPONSORED RESEARCH STATEMENT

Not applicable.

REFERENCE TO MICROFICHE APPENDIX

Not applicable.

FIELD OF THE DISCLOSURE

The invention relates to crosslinked swellable polymers containingcationic sites and stable and labile crosslinkers. Once the cationicsites are exposed on decay of the labile crosslinkers, the polymer willswell and will adsorb to negatively charged surfaces such as sandstonerock. A particularly important use is as fluid diversion agents forsweep improvement in enhanced oil recovery applications and also asdrilling fluids in petroleum production, but applications can alsoinclude uses in the hygiene and medical arts, packaging, agriculture,the cable industry, information technology, in the food industry,papermaking, use as flocculation aids, and the like.

BACKGROUND OF THE DISCLOSURE

The water injection method used in oil recovery is where water isinjected out into the reservoir, usually to increase pressure andthereby stimulate production. Water is injected for two reasons: 1. Forpressure support of the reservoir (also known as voidage replacement).2. To sweep or displace the oil from the reservoir, and push it towardsan oil production well. Normally only 20% of the oil in a reservoir canbe extracted, but water injection increases that percentage (known asthe recovery factor) and maintains the production rate of a reservoirover a longer period of time.

However, sweep recovery is limited by the so-called “thief zones,”whereby water preferentially travels through the more porous regions ofthe reservoirs, bypassing less permeable zones, leaving unswept oilbehind. One means of further improving recovery is to partially blockthief zones with a polymer or other material, thus forcing water throughthe less permeable regions.

U.S. Pat. Nos. 6,454,003, 6,984,705 and U.S. Pat. No. 7,300,973 describean expandable crosslinked polymeric particle having an average particlediameter of about 0.05 to 10 microns (nano-microparticle sizes). Theparticle is highly crosslinked with two crosslinkers, one that is stableand a second that is labile. The excess crosslinking makes the initialparticles quite small, allowing efficient propagation through the poresof a reservoir. On heating to reservoir temperature and/or at apredetermined pH or other stimuli, the reversible (labile) internalcrosslinks break, allowing the particle to further expand by absorbingadditional injection fluid, usually water. The initial polymer issometimes called the “kernel” before its expansion, in analogy to theway a kernel of popcorn “pops” in response to certain stimuli, such asheat.

The unique properties of this particle render it a water-like viscosityat concentrations as high as 1.0% requiring very little horsepower forinjection into the porous media and avoid shearing encountered forstandard polymers. The small particles suspended in water follow thehigh permeability zones—commonly called thief zones or streaks—and thenbe expanded in situ so that the swollen particle blocks the thief zonesand subsequent injections of fluid are forced to enter the remainder ofthe reservoir, more effectively sweeping the reservoir. However, themethod is limited in practice because subsequent water injections alwaysremove some of the polymer. Hence the thief zones become washed out andagain present the problem of allowing the injection fluid to avoid theless permeable zones.

The reason for the washout is not certain, but our own research suggeststhat the swollen polymer is not in gel form, thus although viscous, isstill a liquid that can be washed out of the porous substrate.

What is needed in the art is a long lasting polymer that is lesssusceptible to loss under the conditions of use. In particular, aswellable polymer that partially adsorbs on the rock surface and isresistant to washout by subsequent fluid injections, is needed.

SUMMARY OF THE INVENTION

The invention generally relates to polymers that have stable and labilecrosslinkers, allowing swelling in situ in response to a particularstimulus. Further, the polymers contain cationic sites that becomeaccessible on swelling of the polymer and that act to adsorb to thesurrounding negatively charged surfaces, including, for example, thevarious negatively charged minerals in a reservoir.

Preferably, the polymers of the invention comprise highly crosslinkedexpandable polymeric particles having labile crosslinkers and stablecrosslinkers, wherein at least one of the monomers that makes up thepolymer or copolymer contains cationic sites. To be useful in areservoir application, the polymer must contain sufficient cationicsites so as to allow sorption to rock, thus preventing washout. Inpreferred embodiments, the cationic sites must be at least 0.5 molepercent, or preferably 1, 2, 3, 4, 5, 7.5 or 10 mole percent or evenmore. The cationic site of choice will vary with pH and the mineralconstituents in the reservoir formation, and will also vary withdifferent applications.

The polymer of the invention has particular use in oil recovery, asdescribed above, and is preferably a hydrophilic polymer for thisapplication. However, an adsorbed polymer would find uses in all of thearts where swellable polymers are in current use and polymer loss orwashout is not desired, including as filler for diapers and otherhygiene products, medical devices such as orthopedic insoles, oculardevices, and biomimetic implants, wipe and spill control agents, wireand cable water-blocking agents, ice shipping packs, controlled drugrelease, agricultural uses (e.g., soil additive to conserve water, plantroot coating to increase water availability, and seed coating toincrease germination rates), industrial thickeners, specialty packaging,tack reduction for natural rubber, fine coal dewatering, and the like.

By “polymer” what is meant herein is a polymerized monomer, includingmixtures of two or more different monomers.

A “stable crosslinker” is defined herein to be any crosslinker that isnot degraded under the stimulus that causes the labile crosslinker todisintegrate. Representative non-labile crosslinkers include methylenebisacrylamide, diallylamine, triallylamine, divinyl sulfone,diethyleneglycol diallyl ether, and the like and combinations thereof. Apreferred non-labile crosslinker is methylene bisacrylamide.

The “labile crosslinker” is defined herein to be any crosslinker thatdecays or is reversible on application of a particular stimulus, such asirradiation, suitable pH and temperature, etc. and combinations thereof.Representative labile crosslinkers include acrylate or methacrylateesters of di, tri, tetra hydroxy compounds including ethyleneglycoldiacrylate, polyethyleneglycol diacrylate, trimethylopropanetrimethacrylate, ethoxylated trimethylol triacrylate, ethoxylatedpentaerythritol tetracrylate, and the like; divinyl or diallyl compoundsseparated by an azo such as the vinyl or allyl esters of di or trifunctional acids, and combinations thereof. Preferred labilecrosslinkers include water soluble diacrylates such as polyethyleneglycol diacrylates (PEG 200-1000 diacrylate, preferably PEG 200diacrylate and PEG 400 diacrylate), and polyfunctional vinyl derivativesof a polyalcohol such as ethoxylated (9-20) trimethylol triacrylate andpolymethyleneglycol diacrylate.

US2008075667, herein incorporated by reference, describes additionalacid labile ketal cross linkers that can be used in the invention. Suchacid labile ketal crosslinkers can have one of the following formulas:

wherein n and m are independently an integer of between 1 and 10 andwherein R¹ and R² are independently a lower alkyl and wherein Y is alower alkyl. In particular,2-bis[2,2′-di(N-vinylformamido)ethoxy]propane (BDEP) and2-(N-vinylformamido)ethyl ether (NVFEE) are described and may besuitable in acidic environments, or where the acid is later addedthereto. Such cross linkers can be advantageously combined with themonomers described therein, such as N-vinyl pyrollidone, N-vinylformamide, N-vinylacetamide, N-vinylacetamine, or any other vinyl basedpolymers and copolymers thereof, and may be preferred where theneurotoxic effects of acrylamide are to be avoided.

By “adsorb” what is meant is that the polymer binds to negativelycharged surfaces, however, some amount of absorption is not intended tobe excluded thereby.

The proportion of stable to labile crosslinker can also vary dependingon how much swelling on stimulus is required, but in the enhanced oilrecovery applications a great deal of swelling is desired to effectivelyblock the thief zones and increase the mobilization and/or recovery rateof hydrocarbon fluids present in the formations. Thus, the concentrationof labile crosslinker greatly exceeds the concentration of stablecrosslinker. To obtain sizes in the range of about 0.05 to about 10microns suitable for injection fluid use the crosslinker content isabout 1,000-200,000 ppm of labile crosslinker and from greater than 0 to300 ppm of non-labile crosslinkers.

Combinations of multiple stable and labile crosslinkers can also beemployed advantageously. Reaction to stimuli can also be controlled bylabile crosslinker selection, as needed for particular reservoirconditions or for the application at issue. For example, judiciousselection of labile crosslinkers—one that degrades at a very hightemperature and another at a lower temperature—can affect thetemperature and pH at which the kernel pops. Furthermore, labilecrosslinker concentration can be manipulated to obtain popping at adesired time and temperature.

Other crosslinkers include, but are not limited to, diacrylyl tertiaryamides, diacrylylpiperazine, DATD (diallyltartardiamide), DHEBA(dihydroxyethylene-bis-acrylamide), and BAC (bis-acrylylcystamine),trimethylolpropane trimethacrylate (TMPTMA), propyleneglycol triacrylate(PGTA), tripropyleneglycol diacrylate (TPGDA), allyl methacrylate (AMA),triethyleneglycol dimethacrylate (TEGDMA), tetrahydrofurfurylmethacrylate (TFMA) and trimethylolpropane triacrylate (TMPTA).Multifunctional crosslinkers include, but are not limited to,pentaerythritol triacrylate, 1,5 pentane diol dimethacrylate, andpentaerythritol triallylether.

By “cationic site” what is meant is a site in the polymer that is netpositively charged under the conditions of use. The polymer can be madewith cationic monomers, and this is preferred for downhole applications,as this ensures that cationic sites are well dispersed throughout theparticle and chemical modifications inside the reservoir may bedifficult. However, in applications where access is unrestricted, thepolymer may be treated after synthesis to convert the polymer to acationic polymer. For example, the cationic polyacrylamide can be aMannich modification product of polyacrylamide, a Hofmann degradationproduct of polyacrylamide, a reaction product between partiallyhydrolyzed polyacrylamide and polyethyleneimine, and the like.

Cationic polymers are typically used as flocculants or to bind to andseparate various minerals. Therefore, much is known in the art about theselection of the appropriate cations for adsorption to particularminerals. See e.g., Youjun Deng, et al., Adsorption of Polyacrylamide onSmectite, Illite, and Kaolinite, Soil Sci Soc Am J 70:297-304 (2006).

Preferred cationic sites include quaternary ammonium sites, such asthose found in diallyldimethylammonium chloride (DADMAC),(3-(methacryloylamino) propyl) trimethyl ammonium chloride (MAPTAC),(2-(methacryloyloxy) ethyl) trimethyl ammonium chloride (MATMAC), andvinylbenzyl trimethyl ammonium chloride (VBTMAC).

In another embodiment, the cationic polymers are selected from the groupconsisting of DMAEA/MCQ (dimethylaminoethylacrylate methyl chloridequaternary salt), DMAEA/BCQ (dimethylaminoethylacrylate benzyl chloridequaternary salt), and DMAEM/MCQ (dimethylaminoethylmethacrylate methylchloride quaternary salt). Many other representative cationic monomersare described throughout the patent literature, e.g., EP1734011, whichis incorporated by reference herein.

The solvent of the system is an aqueous liquid, such as deionized water,potable water, fresh water, or brine having a total dissolved solidsconcentration up to the solubility limit of the solids in water. Inertfillers known in the art may also be added to the system if desired orfor use as proppants. Such fillers include crushed or naturally finerock material or glass beads, sand and the like.

Representative nonionic monomers include acrylamide,N-isopropylacrylamide, N,N-dimethylacrylamide, N,N-diethylacrylamide,dimethylaminopropyl acrylamide, dimethylaminopropyl methacrylamide,acryloyl morpholine, hydroxyethyl acrylate, hydroxypropyl acrylate,hydroxyethyl methacrylate, hydroxypropyl methacrylate,dimethylaminoethylacrylate (DMAEA), dimethylaminoethyl methacrylate(DMAEM), maleic anhydride, N-vinyl pyrrolidone, vinyl acetate andN-vinyl formamide. Preferred nonionic monomers include acrylamide,N-methylacrylamide, N,N-dimethylacrylamide and methacrylamide. N-vinylformamide, N-vinylacetamide, N-vinylacetamine and copolymers may bepreferred with the acid labile ketal crosslinkers of US2008075667.

Anionic or betaine monomers can be combined with the polymers of theinvention, but their use is not preferred as they would compete forbinding to the cationic sites. However, small amounts may be acceptableprovided the cationic sites predominate.

The particles can be prepared by methods known in the art, including theinverse emulsion polymerization technique described in U.S. Pat. Nos.6,454,003, 6,729,402 and U.S. Pat. No. 6,984,705. Particle suspensionsare prepared by mixing the particles and injection fluid or by mixingparticles in an inverse suspension with a surfactant/and or shearing andadditional injection fluid if needed.

In addition to the polymers having cationic sites and fluid, the aqueoussolution may also contain other conventional additives includingchelating agents to remove polymerization inhibitors, pH adjusters,initiators and other conventional additives, accelerators, retardants,surfactants, stabilizers, etc., as appropriate for the particularapplication.

In one embodiment, the invention is a composition comprising a fluid,and expandable polymeric particles having at least 0.5 mole percentcationic sites and both labile and stable crosslinkers. In anotherembodiment, the invention is a composition comprising expandablepolymeric particles having cationic sites and both labile and stablecrosslinkers, said particle combined with a fluid that allows thepolymer to swell, exposing the cationic sites, and allowing the swelledpolymer to adsorb to the negatively charged minerals in the reservoirand be resistant to washout.

In another embodiment, the invention is a composition comprising highlycrosslinked expandable polymeric particles having at least 0.5 molepercent cationic sites, an unexpanded volume average particle sizediameter of from about 0.05 to about 10 microns and a crosslinking agentcontent of from about 1,000 to about 200,000 ppm of labile crosslinkersand from greater than 0 to about 300 ppm of stable crosslinkers.

In another embodiment, the invention is a method of increasing therecovery of hydrocarbon fluids in a subterranean formation comprisinginjecting into the subterranean formation a composition comprising afluid, and a highly crosslinked expandable polymeric particle having atleast 0.5 mol percent cationic sites, wherein polymeric particle has anunexpanded volume average particle size diameter of 0.05-10 microns anda crosslinker content of about 1,000-200,000 ppm of labile crosslinkerand about greater than 0 to 300 ppm of stable crosslinker, saidpolymeric particle has a smaller diameter than the pore throats of thesubterranean formation, and said labile crosslinkers break under theconditions of temperature and a suitable pH in the subterraneanformation to allow the polymeric particle to expand, thus exposing thecationic sites so that said particle can adsorb to the negativelycharged minerals in the formation.

In preferred embodiments, the polymeric particles are made with at least0.5 mole percent cationic monomer, the stable crosslinker can bemethylene bisacrylamide, and the labile crosslinker can be apolyethylene glycol diacrylate or2-bis[2,2′-di(N-vinylformamido)ethoxy]propane (BDEP) and2-(N-vinylformamido)ethyl ether (NVFEE).

DESCRIPTION OF EMBODIMENTS OF THE INVENTION

The invention provides a novel polymer containing cationic sites thatswells on stimulus and is then adsorbed to the surrounding surfaces viathe cationic sites. Such polymers have particular utility in sweepingreservoirs, but many uses are possible.

EXAMPLE 1 Prior Art

We ran a number of slim tube tests in which we injected about 1 porevolume of BRIGHTWATER® (NALCO™, copolymer of acrylamide and sodium AMPScrosslinked with methylene bis-acrylamide and PEG diacrylate)micro-particles into 40 inch slim tubes packed with sand. The sand packwas then heated (150-190° F.) to allow the polymer to pop. Afterwards,water was injected into the sand packs and the resistance to the flow ofwater measured. While the popped polymers initially exhibited goodresistance factors, this behavior appeared to washout with additionalwater injection. Typically within one pore volume of water injection theResidual Resistance Factor (RRF) dropped to a number about 1-2. Thisbehavior was observed with slim tubes which were packed with 6.7 Darcysand as well as 1 Darcy sand. Therefore, the treatment effect in porousmedia with these micro-particles was only temporary.

EXAMPLE 2 Invention

Since the prior art polymer is subject to washout, we propose that whencombined with sufficient cationic sites, such as —NH3+ (quaternaryammonium salt monomers), the resulting polymer will remain stable towashout because the polymer will strongly adsorb to the negativelycharged minerals in the formation. We intend to prepare a polyacrylamidecopolymer having 0.5%, 1%, 2%, 5% and 10% of a cationic monomer, andrepeat the experiments above. We predict that a sand pack treated withpolymers having cationic sites will exhibit reduced flow.

In summary, polymers that can be adsorbed to media having negativecharges can be made by the inclusion of at least 0.5 mol percentcationic sites to a particle having been over-crosslinked with methylenebisacrylamide and PEG diacrylates.

The following references are incorporated by reference herein in theirentirety:

U.S. Pat. Nos. 6,454,003, 6,729,402 and 6,984,705

US2008075667

U.S. Pat. No. 3,727,688

U.S. Pat. No. 4,068,714

U.S. Pat. No. 3,749,172

U.S. Pat. No. 4,683,949

EP1734011

Youjun Deng, et al., Adsorption of Polyacrylamide on Smectite, Illite,and Kaolinite, Soil Sci Soc Am J 70:297-304 (2006).

The invention claimed is:
 1. A method of increasing the recovery ofhydrocarbon fluids in a subterranean formation comprising injecting intoa subterranean formation a composition comprising water, and a highlycrosslinked expandable hydrophilic polymeric particle having at least0.5 mole percent cationic sites, wherein: i) said polymeric particle hasan unexpanded volume average particle size diameter of 0.05-10 micronsand a crosslinker content of about 1,000-200,000 ppm of labilecrosslinker and about greater than 0 to 300 ppm of stable crosslinker,ii) said polymeric particle has a smaller diameter than the pore throatsof the subterranean formation, iii) said labile crosslinkers break underthe conditions of temperature and suitable pH in the subterraneanformation to allow the polymeric particle to expand, and iv) saidcationic sites adsorb to said subterranean formation thus making saidparticle resistant to washout.
 2. The method of claim 1, wherein thecationic sites are provided by at least one cationic monomer selectedfrom the group consisting of diallyldimethylammonium chloride,(3-(methacryloylamino) propyl) trimethyl ammonium chloride,(2-(methacryloyloxy) ethyl) trimethyl ammonium chloride, vinylbenzyltrimethyl ammonium chloride, dimethylaminoethylacrylate methyl chloridequaternary salt, dimethylaminoethylacrylate benzyl chloride quaternarysalt, and dimethylaminoethylmethacrylate methyl chloride quaternarysalt.
 3. The method of claim 1, wherein the polymeric particle comprisescationic polyacrylamide, the stable crosslinker comprises methylenebisacrylamide, and the labile crosslinker comprises a polyethyleneglycol diacrylate or 2-bis[2,2′-di(N-vinylformamido)ethoxy]propane.